1. Field of the Invention
The present invention relates to a DC-to-DC conversion apparatus, and more particularly to a multi-output DC-to-DC conversion apparatus with a voltage-stabilizing function.
2. Description of Prior Art
For a variety of electronic products, providing the most suitable DC voltage level for themselves has become a necessary trend. Thus, a useful method of converting the standard supply voltage into a required voltage for load is necessary, and which should satisfy general-purpose, high-efficiency, and high-reliability requirements. Because most electronic products, such as televisions, audios, computers, are supplied with DC-voltage electricity, the utility-line AC voltage has to be converted into DC voltages of various levels to make the electronic products perform properly.
Reference is made to FIG. 1 which is an architecture block diagram of a prior art power supply. The power supply mainly includes an EMI filter 10A, a rectifier 20A, a power factor corrector 30A, a DC-to-DC converter 40A, and a buck converter 70A. The DC-to-DC converter 40A has a plurality of power switches (not shown) and a main transformer (not shown). The EMI filter 10A is electrically connected to an AC source Vs to eliminate the conducted EMI noises in the AC lines. Therefore, in case of possible interference for different apparatuses connected to the power supply in the same distribution system could be restrained. The rectifier 20A is electrically connected to the EMI filter 10A to convert AC supply outputted form the EMI filter 10A to DC supply. The power factor corrector 30A is electrically connected to the rectifier 20A to improve the power factor of the power supply. The DC-to-DC converter 40A is electrically connected to the power factor corrector 30A to provide a voltage for the main transformer by controlling the power switches though a PWM control scheme. Therefore, the outputted DC supply of the power factor corrector 30A can be provided from the primary winding of the main transformer to the secondary winding thereof for energy conversion. The buck converter 70A is electrically connected to an output terminal Vo1 of the DC-to-DC converter 40A to provide a lower DC voltage.
The most popular power supplies provide +12V, +5Vsb, +5V, and +3.3V output voltages, which are supplied to desktop computers. For high-efficiency applications, the +12V output voltage (labeled as Vo1 in FIG. 1) is converted from the main transformer; whereas, the +5V output voltage (labeled as Vb1) and the +3.3V output voltage (labeled as Vb2) are obtained by converting the +12V voltage by the buck converter 70A. More particularly, the +12V voltage is more than two times as higher as the +5V (and even more than three times as higher as the +3.3V). Accordingly, a large voltage difference between the input voltage and the output voltage of the buck converter 70A would increase core losses of the internal magnetic components and switching losses of the power switches. Therefore, the efficiency of the buck converter 70A is reduced, particularly in much higher frequency operations.
Accordingly, it is desirable to provide a multi-output DC-to-DC conversion apparatus with a voltage-stabilizing function to provide lower-level voltage functioned as an input voltage to the buck converter, thus increasing efficiency of the buck converter.